DIAMOND POWDER IN THE MACHINE SHOP THE diamond used for this purpose, costing 85 cents per carat, is an inferior grade of diamond, not so hard as the black diamond used for drills and truing emery wheels, and not of a clear and perfect structure to permit it to enter the gem class. Many are a mixed black and white, others yellow and some pink; many are clear but flaky. Then there is the small débris from diamond cutting, which is reduced to powder and sells somewhat cheaper; but some find it more economical to use the above and powder it themselves, as the débris from diamond cutting is of a flaky nature, and does not charge into the lap so well. Assuming there is 25 carats to reduce to powder, proceed as follows: Into a mortar, as shown at Fig. 12, place about 5 carats, using an 8-ounce hammer to crush it. It takes from 3 to 4 minutes' steady pounding to reduce it to a good average. Scrape the powder free from the bottom and the sides and empty into one-half pint of oil. The oil used is the best olive oil obtainable, and is held in a cupshaped receptacle that will hold a pint and one half. The 25 carats being reduced to powder, and in the oil, stir it until thoroughly mixed, and allow to stand 5 minutes; then pour off to another dish. The diamond that remains in the dish is coarse and should be washed in benzine and allowed to dry, and should be repounded, unless extremely coarse diamond is desired. In that case label it No. o. Now stir that which has been poured from No. o, and allow to stand 10 minutes. Then pour off into another dish. The residue will be No. I. Repeat the operation, following the table below. The settlings can be put into small dishes for convenient use, enough oil staying with the diamond to give it the consistency of paste. The dishes can be obtained from a jewelers' supply house. Diamond is seldom hammered; it is generally rolled into the metal. For instance, several pieces of wire of various diameters charged with diamond may be desired for use in die work. Place the wire and a small portion of the diamond between two hardened surfaces, and under pressure roll back and forth until thoroughly charged. No. 2 diamond in this case is generally used. Or one can form the metal any desired shape and apply diamond and use a roll, as Fig. 14, to force the diamond into the metal. This is then a file which will work hard steel, but the moment this diamond file, or lap, is crowded it is stripped of the diamond, and is consequently of no use. It is to be used with comparatively light pressure. Diamond Laps COPPER is the best metal. It takes the diamond readily, and retains it longer than other metals; brass next, then bessemer steel. The latter is used when it is wished to preserve a form that is often used. FIG. 13 FIG. 14 FIG. 15 FIG. 12 Diamond Laps and Tools For sharpening small, flat drills, say 0.008 to 0.100, a copper lap mounted on a taper shank, as in Fig. 13, and charged on the face with No. 2 diamond, using pressure on the roll, makes a most satisfactory method of sharpening drills. The diamond lasts for a long time if properly used, and there is no danger of drawing the temper on the drill. It is much quicker than any other method of sharpening. To charge the lap use the roll, Fig. 15, supported on a T rest pressing firmly against the lap, being careful to have the roll on the center; otherwise instead of charging the lap it will be grinding the roll. The diamond may be spread either on the lap or the roll, and the first charging usually takes twice the amount of diamond that subsequent charging takes. To avoid loss of diamond, wash the lap in a dish of benzine kept exclusively for that purpose. This can be reclaimed by burning the metal with acids, and the diamond can be resettled. For the grinding of taper holes in hard spindles or for position work in hard plates, where holes are too small to allow the use of emery wheels, No. 1 diamond does the work beautifully. Or if it is wished to grind sapphire centers or plugs as stops, etc., a bessemer lap made in the form of a wheel and charged with diamond on the diameter does the work nicely. Nos. 5 and 6 diamond are used on boxwood laps, mounted on taper plugs or chucks, and the diamond smeared on with the finger. The lap is run at high speed and used for fine and slow cutting which also gives a high polish. A FIG. 16. Cross-section of REAMER AND CUTTER GRINDING Reamer Clearances AFTER Constant experimenting for a period of more than a year, the Cincinnati Milling Machine Company succeeded in establishing tables for four styles of reamers for obtaining what they consider to be the best clearances, the object being to grind clearances on reamers which would ream the greatest number of smooth holes with a minimum amount of wear. The four styles of reamers are as follows: Hand reamers for steel, hand reamers for gray iron and bronze, chucking reamers for gray iron and bronze, chucking reamers for steel. The company uses adjustable blade reamers almost exclusively, all of which are ground in the toolroom on their universal cutter and tool grinder. Fig. 16 is a cross-section of a hand reamer. Two clearance lines, A and B, are ground on the blades, a being the cutting clearance and b the second clearance called for in the table. The object of giving the adjustment for the second clearance so minutely is to provide a proper width of land, which equals .025 inch on all hand reamers for gray iron or bronze, and 0.005 inch on hand reamers for steel. FIG. 17. Chucking Reamer Chucking reamers for gray iron and bronze have, in this system, 23degree beveled ends as shown in Fig. 17, and are provided with two clearances along the blades, for which the settings are given in Table 3. The beveled ends have only one clearance which is equal to the second clearance given in Table 3. Fig. 18 shows a chucking reamer for reaming steel. In these reamers the blades are circular ground to the exact size of hole to be reamed and without clearance, the 45degree beveled ends only having clearance as given in Table 4. On all reamers of this style the blades are ground from .015 to .020 inch below size half of their length toward the shank end. प FIG. 18. Chucking Reamer In grinding the clearances for the various kinds of reamers as given in Tables 1, 2, and 3, the tooth rest is held stationary on the emery wheel head of the grinder, while in grinding the 45-degree beveled ends on the chucking reamers for steel, the tooth rest is supported from the grinder table and travels with the work. The front end of the hand reamer blades are tapered about 0.004 per inch. The back ends of the blades are also slightly tapered to prevent injuring the holes when backing the reamer out. |